.TH gethostlatency.bt 8  "2018-09-08" "USER COMMANDS"
.SH NAME
gethostlatency.bt \- Show latency for getaddrinfo/gethostbyname[2] calls. Uses bpftrace/eBPF.
.SH SYNOPSIS
.B gethostlatency.bt
.SH DESCRIPTION
This traces and prints when gethostbyaddr(), getaddrinfo(), gethostbyname(),
and gethostbyname2() are called, system wide, and shows the responsible PID and
command name, latency of the call (duration) in milliseconds, and the host
string.

This tool can be useful for identifying DNS latency, by identifying which
remote host name lookups were slow, and by how much.

This tool currently uses dynamic tracing of user-level functions and registers,
and may need modifications to match your software and processor architecture.

Since this uses BPF, only the root user can use this tool.
.SH REQUIREMENTS
CONFIG_BPF and bcc.
.SH EXAMPLES
.TP
Trace host lookups (getaddrinfo/gethostbyname[2]) system wide:
#
.B gethostlatency.bt
.SH FIELDS
.TP
TIME
Time of the command (HH:MM:SS).
.TP
PID
Process ID of the client performing the call.
.TP
COMM
Process (command) name of the client performing the call.
.TP
LATms
Latency of the call, in milliseconds.
.TP
HOST
Host name string: the target of the lookup.
.SH OVERHEAD
The rate of lookups should be relatively low, so the overhead is not expected
to be a problem.
.SH SOURCE
This is from bpftrace.
.IP
https://github.com/bpftrace/bpftrace
.PP
Also look in the bpftrace distribution for a companion _examples.txt file containing
example usage, output, and commentary for this tool.

This is a bpftrace version of the bcc tool of the same name. The bcc tool
provides command line options.
.IP
https://github.com/iovisor/bcc
.SH OS
Linux
.SH STABILITY
Unstable - in development.
.SH AUTHOR
Brendan Gregg
.SH SEE ALSO
tcpdump(8), gethostbyname(3), getaddrinfo(3)
